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Chapters 11: Introduction to the Nervous System and Nervous Tissue

Nervous system – controls our perception and experience of world

Directs movement

Seat of consciousness, personality, learning, and memory

Regulates

Module 11.1: Overview of the Nervous System

[2 Anatomical Div. = CNS, PNS]

1. – includes brain and spinal cord

2. – consists of all nerves in body outside protection of skull and vertebral column (cranial nerves, spinal nerves)

[3 Functional Div. = Sensory, Integrative, Motor]

1.

– sensory receptors gather information about internal and external environments

- afferent division carries information toward CNS

a. sensory division

– signals from , bones, joints, and skin;

- special sensory div. (vision, hearing, taste, smell, and balance)

b. sensory division

– signals from (organs)

2. functions – analyze and interpret incoming sensory information and determine response

Anatomical Divisions of the Nervous System

Functional Divisions of the Nervous System

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3. functions

– actions performed in response to integration

- division carries information away from CNS

a. nervous system – info to skeletal muscle

b. nervous system (ANS) – information to smooth muscle, cardiac

muscle, glands

Module 11.2: Nervous Tissue

Neurons – excitable cell type responsible for sending and receiving signals in form of action potentials (AP)

A. Structure of neurons

1.

nucleus, cytoplasm with organelles, (RER, gray color)

2. Cytoplasmic extensions (processes):

– receive information from other neurons, conduct impulse toward soma

(nerve fiber) – conducts impulse away from soma, includes axon hillock, axon terminals (synaptic knobs)

Poliovirus and Retrograde Axonal Transport

• – caused by poliovirus; infection that impacts CNS (especially SC) à deformity and paralysis

• No cure exists, but prevented by vaccination

• Virus accesses CNS by entering muscle cells à motor neurons at NMJ à

retrograde axonal transport until reaching SC

• Other viruses (herpes simplex, rabies) and toxins (tetanus) can to invade via this method

Neurons

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• Structural:

neurons – single axon and multiple dendrites, > 99% of all neurons

(motor)

neurons – one axon, one dendrite, and cell body between them; found in eye and olfactory epithelium (sensory)

neurons – have only one fused axon that extends from cell body and divides into two processes (sensory)

• Functional :

(afferent neurons) – carry information toward CNS; pseudounipolar or bipolar

(association neurons) – relay information within CNS between sensory and motor neurons; make up most of neurons in body; multipolar

(efferent neurons) – carry information away from cell body in CNS to muscles and glands; multipolar

• Specific neuron components group together:

CNS:

– clusters of neuron cell bodies

– bundles of axons

PNS:

– clusters of neuron cell bodies

– bundles of axons

Classification of Neurons

Neurons

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• – provide support and protection for neurons, maintain their

environment, divide and fill space when a neuron dies

- CNS:

• Oligodendrocytes

• Ependymal cells

- PNS:

• Schwann cells

•

• CNS:

– large star-shaped cells

Facilitate transport of nutrients and gases between blood vessels and neurons; form blood-brain barrier (BBB)

- – form myelin in CNS

- – activated by injury into phagocytic cells

- cells – ciliated cells that manufacture and circulate CSF

• PNS:

- cells – produce myelin

- cells – supportive functions

= repeating layers of phospholipid plasma membrane, insulation

Nodes of Ranvier = gaps between myelin sheaths

= myelinated axons

= neuron cell bodies, unmyelinated processes

Neuroglia

The Myelin Sheath

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Regeneration nearly nonexistent in CNS and is limited in PNS

• Regeneration steps:

1. Degeneration of axon and myelin sheath distal to injury (Wallerian

degeneration)

2. from proximal end of axon

3. Schwann cells form regeneration tube

4. Single growth process grows into regeneration tube

5. New axon is to its target cell

Gliomas and Astrocytomas

• Primary brain tumors – originate in brain; most are (caused by abnormally high rate of division of glial cells)

• Predisposing conditions – exposure to ionizing radiation and certain diseases

• Most commonly affected cell is à tumor is called

Range in severity from mild with good prognosis to highly aggressive with very poor prognosis

Treatment – varies with tumor type, age, and health of patient; usually involves

surgical removal of mass with chemotherapy and perhaps radiation therapy

Module 11.3: Electrophysiology of Neurons

• All neurons are excitable or responsive to stimuli (chemical, electrical, and mechanical)

• Stimuli generate electrical changes across plasma membrane (PM)

potentials – travel short distances

potentials – travel entire length of axon; begin at trigger zone à

axon terminal

Regeneration of Nervous Tissue

Introduction to Electrophysiology of Neurons

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• Ion channels – ions must rely on specific protein channels for diffusion

• Resting Membrane Potential (RMP) = -

due to difference in distribution of ions across PM

- Ions follow conc. gradient

- Open in response to specific chemical binding

- Open or close due to changes in voltage across PM

- Open or close due to mech. stim. (stretch, press., vibration)

RMP =

Cell is polarized (positive on outside, negative on inside of PM)

Diffusion of ions across PM determined by Electrochemical Gradient:

• Electrical gradient:

on , on of plasma membrane

• Chemical Gradient:

outside > Na+ inside

inside > K+ outside

How Do Positive Ions Create a Negative Resting Membrane Potential

• A neuron that has no membrane potential; charges are distributed equally across plasma membrane

• Now, imagine that a potassium ion diffuses out of cytosol down concentration gradient through a leak channel…

• Six positive charges are now outside membrane and four positive charges inside; makes overall charge inside cytosol –1 and in extracellular fluid +1—a membrane potential has been created

Principles of Electrophysiology: Types of Ion Channels

Principles of Electrophysiology

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• Imagine that many thousands of potassium ions exit through leak channels; causes

membrane potential to become progressively more negative

Changes in Resting Membrane Potential: Ion Movements:

• –Na+ channels open, Na+ flow into cell; membrane potential becomes more positive

• – K+ ion channels open; K+ flow out of cell; cell becomes more negative, returning to RMP

• – cell becomes more negative than normal RMP due to efflux of K+ plus influx of Cl-

potentials – serve as triggers for long-distance AP

• May cause:

– positive charges enter cytosol and make membrane potential less negative ( -70 to -60 mV)

– either positive charges exit or negative charges enter cytosol; makes membrane potential more negative (-70 to -80 mV)

• Sometimes called potentials because vary greatly in size

• Events in an Action Potential:

1. Local potential must be able to depolarize axon strongly enough to reach (usually -55 mV)

2. Depolarization – sodium ions rush in ( )

3. – potassium ions rush out ( )

4. Hyperpolarization may occur

Local Potentials

Action Potentials

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Local Anesthetic Drugs

• Local anesthetics – (like ) commonly administered agents for surgical or dental procedures; produce temporary numbness in specific area

• Block voltage-gated sodium channels of neurons in treated area; prohibits depolarization and therefore action potentials relaying pain are not transmitted to CNS

• Nonselective; also affect sodium channels in muscles of area; causes temporary paralysis; reason for crooked smiles and drooling following dental work

• period – period of time, after neuron has generated an AP, when neuron cannot be stimulated to generate another AP

• refractory period – when no additional stimulus (no matter how strong) is able to produce additional AP

• refractory period – immediately after absolute refractory period; only a strong stimulus can produce AP

Graded local potentials produce variable changes in membrane potentials

potentials cause a maximum to +30 mV

• All-or-none principle – AP that either happens completely or not at all

If a neuron does not depolarize to threshold then no AP will occur

AP are not dependent on strength, frequency, or length of stimulus like local potentials

APs conducted ( ) along entire length of axon =

– unidirectional

– Each AP triggers next section of axon, usually starting at trigger zone and ending at axon terminals

Refractory Period

Local and Action Potentials Compared

Propagation of Action Potentials

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Conduction speed – influenced by both axon diameter and presence or absence

of myelination

–

– Presence or absence of gives rise to 2 types of conduction:

– conduction – myelinated processes exhibit “jumping” type of conduction, rate

– conduction – unmyelinated processes, rate of conduction

Saltatory conduction –myelinated axons increase speed of conduction; AP only

depolarize nodes of Ranvier and “jump over”

Continuous conduction – in unmyelinated axons every section of axolemma from trigger zone to axon terminal must propagate AP; slower conduction speed

• Classification of Axons by Conduction Speed:

Type A fibers – diameter (120 m/sec or 250 mi/h); (5–20 µm) and ; sensory and motor axons associated with skeletal muscle and joints

Type B fibers – diameter, slower conduction speeds (15 m/sec or 32 mi/hr); mostly with intermediate diameter axons (2–3 µm); ANS efferent fibers, some sensory

Type C fibers – diameter, slowest conduction speeds (0.5–2 m/sec or 1–5 mi/hr); (0.5–1.5 µm); ANS efferent fibers and sensory axons (transmit pain, temperature, and pressure)

Multiple Sclerosis

• Multiple sclerosis (MS) – certain cells of immune system attack myelin sheaths within CNS; type of (patient’s own immune system attacks part of body)

• Causes progressive loss of myelin sheath; in turn causes loss of current from neurons

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• Symptoms – result from progressive slowing of AP propagation; symptoms depend

on region of CNS affected; most exhibit changes in sensation (e.g., numbness), alterations in behavior and cognitive abilities, and motor dysfunction, including paralysis

Module 11.4: Neuronal Synapsis

• – where a neuron meets its target cell (in this case another neuron) is called a neuronal synapse

- electrical (gap junctions) – breathing, cardiac & SMC

- – most synapses

– can occur between an axon of one neuron and another part of another neuron (dendrite, soma, axon)

– Presynaptic neuron à à Postsynaptic neuron

• Events at a Chemical Synapse:

- multiple neurons secreting many different types of excitatory or inhibitory neurotransmitters

1. AP in presynaptic neuron triggers ion channels in axon terminal to open

2. of calcium ions causes synaptic vesicles to release

neurotransmitter into synaptic cleft

3. Neurotransmitters bind to on postsynaptic neuron

4. Ion channels open, leading to a local potential and possibly an AP if threshold

is reached

Postsynaptic potentials – can be Excitatory or Inhibitory:

a. Excitatory postsynaptic potential (EPSP) = Membrane potential moves to threshold

b. Inhibitory postsynaptic potential (IPSP) = Membrane potential moves

away from threshold

Overview of Neuronal

Chemical Synapses

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Arthropod Venom

• Venomous arthropods (in United States) include spiders and scorpions; many of their venoms affect neuronal synapses; termed neurotoxins

• (Latrodectus mactans) – toxin causes massive release of neurotransmitter leading to repetitive stimulation of postsynaptic neuron

• – most lethal of 40 species in United States; venom prevents postsynaptic sodium channels from closing; membrane remains polarized and continues to fire action potentials

• Mechanisms are different but result is similar; both lead to overstimulation of postsynaptic neuron;

• Common symptoms – muscle hyperexcitability, sweating, nausea and vomiting, and difficulty breathing

• Treatment and prognosis – depends on amount of venom received and availability of medical care; severe cases usually require to block effects of toxin

– Neurons receive input, both inhibitory and excitatory, from multiple neurons, each of

which influences whether an action potential is generated

– – process in which postsynaptic neuron integrates all incoming information into a single effect

Module 11.5: Neurotransmitters

• Over 100 known neurotransmitters

4 groups:

1. (acetylecholine)- E [ ]

Neural Integration

Neurotransmitters

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2. Biogenic amines: E

Catecholamines (NE, Epi (adrenaline), dopamine) [ ]

Serotonin

3. Amino acids: (Glutamate – E; GABA- Inhib.)

4. Neuropeptides: E and I (endorphins)

Psychiatric Disorders and Treatments

• Psychiatric disorders affect thought processes; generally treated by modifying synaptic transmission to change how neurons communicate

• Psychopharmacology (study of drugs that affect higher brain functions) targets either AP generation or some aspect of neurotransmitter physiology:

– repetitive psychotic episodes (periods during which patient is unable to appropriately test beliefs and perceptions against reality); thought to result from excessive release of dopamine; management involves blocking postsynaptic dopamine receptors

disorders – marked by disturbances in mood; decreased levels of serotonin, norepinephrine, and/or dopamine; most widely used antidepressants are selective serotonin reuptake inhibitors (SSRIs)

– characterized by exaggerated and inappropriate fear responses; abnormalities in norepinephrine, serotonin, and GABA transmission; drugs for treatment include antidepressants, GABA activity enhancers

– characterized by episodes of abnormal elevated mood (mania) followed by depression; treatments involve decreasing ease of AP generation

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Module 11.6: Functional Groups of Neurons

• Groups of interneurons within CNS:

• Composed of neuroglial cells, dendrites, and axons in one location and cell bodies in another location

• Connections between pools allow for complex mental activity (planned movement, cognition, and personality)

- Neural circuits – patterns of synaptic connection between neural pools

- circuits

- one neuron sends impulses to multiple postsynaptic neurons

- incoming sensory information sent from SC to different neuronal pools in brain for processing

- circuits

- axon terminals from multiple neurons converge onto a single postsynaptic

neuron - respond to sensory information

Neuronal Pools

Neuronal Circuits

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Chapter 12: The Central Nervous System

CNS =

- involved in movement, interpreting sensory, maintaining homeostasis, and functions relating to mind

Module 12.1: Overview of the Central Nervous System

• Functions of nervous system:

• functions muscles contract, glands secrete (PNS)

• functions –sensations in and outside body (PNS)

• functions – include decision-making processes (CNS)

• Interpretation of sensory information

• Planning and monitoring movement

• Maintenance of homeostasis

• Higher mental functions such as language and learning

• Brain – soft, whitish-gray organ in cranial cavity, continuous with SC

- mostly nervous tissue; some epithelial and CT

• filled with cerebrospinal fluid ( )

• ~20% of cardiac output; requires large amounts of O2, glucose, and nutrients

4 divisions of brain:

•

- left and right hemispheres

- higher mental functions, sensory & motor

Overview of CNS Functions

Basic Structure of the Brain and SC

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• - deep to hemispheres

- process, integrate & relay; homeostasis; bio rhythms

• - inferior to occipital lobe

- voluntary motor activities

• = midbrain, pons, medulla oblongata

- reflexes, homeostasis, relay information

– located in vertebral cavity

- Extends from foramen magnum to L1 & L2

- Length ~ 45 cm (17–18 inches)

- Diameter 0.65–1.25 cm (0.25–0.5 inches)

- – CSF filled cavity within SC, continuous with brain’s ventricles

White matter – found in both brain and SC; ( axons)

= bundles of white matter (processes in CNS)

= clusters of cell bodies and dendrites (gray matter)

matter – found in both brain and SC;

(cell bodies, dendrites, and unmyelinated axons)

1. Cerebral cortex is gray matter

2. Center H (butterfly)-shape of SC

Module 12.2: The Brain

• – shallow grooves on surface of cerebrum

• - elevated ridges found between sulci

• Corpus callosum – connects right & left hemispheres

The Cerebrum

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• fissure – deep groove that separates left and right cerebral

hemispheres • Transverse fissure – separates occipital lobe from cerebellum

• – CSF-filled cavities, one in each hemisphere

• Five lobes are found in each hemisphere:

o Frontal lobe (motor, complex mental fcn.) o Parietal lobe ( ) o Temporal lobe ( ) o Occipital lobe ( ) o Insula ( )

• Cerebral Cortex = gray matter, covers cerebral hemispheres

• All neurons in cortex are interneurons

• Functions of neocortex (most recently evolved part of brain) include conscious

processes as planning movement, interpreting incoming sensory information, and complex higher functions

• Gray Matter: Cerebral Cortex:

o Neocortex is divided into three areas: [Motor, Sensory, Association] 1. motor cortex – plans and executes movement

- located in frontal lobe (pre-central gyrus)

▪ cortex – anterior to primary motor cortex, plan and

carry out movement

▪ eye fields -back and forth eye movements as in reading

2. Primary sensory cortices – receive and process sensory input

▪ Somatosensory areas– in postcentral gyrus of parietal lobe;

cutaneous (temp. & touch) ▪ Visual areas –

▪ Auditory areas –

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▪ Gustatory cortex – insula and parietal

▪ Olfactory cortex –

3. Association areas integrate different types of information ▪ – produce speech sounds

▪ Prefrontal cortex – most of frontal lobe, fcn. in behavior, personality,

learning, memory

▪ Parietal & temporal association cortices – integrate sensory info,

attention

• Basal nuclei

- masses of gray matter deep within each hemisphere

-

- Caudate nuclei

- Putamen

- Globus pallidus

• Limbic system

- includes limbic lobe, hippocampus, amygdala

- connect these regions of gray matter with rest of brain

– Found only within mammalian brains

–

Diencephalon – located in center of brain between hemispheres above brainstem

• 4 parts: Thalamus, Hypothalamus, Epithalamus, Subthalamus

•

The Diencephalon

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Gateway for sensory info. to cerebral cortex

Receives all sensory (except smell)

•

Regulation of ANS, sleep/wake cycle, thirst and hunger, and body temperature

Secretes hormones that reg. pituitary & other glands

• – superior to thalamus; includes endocrine gland called pineal gland that secretes melatonin; hormone involved in sleep/wake cycle

• – inferior to thalamus; functionally connected with basal nuclei; together, they control movement

Cerebellum

- located inferior to occipital lobe

-

- arbor vitae

Brainstem

-

- vital to our immediate survival

- Includes midbrain, pons, medulla oblongata

•

- surrounds cerebral aqueduct (connects third and fourth ventricles)

- Superior and inferior : involved in visual and auditory relexes respectively

- Substantia nigra – works with basal nuclei to control movement; produces dopamine

• – inferior to midbrain

Cerebellum

The Brainstem

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- Regulation of movement, breathing, reflexes, and complex functions

associated with sleep and arousal

• – most inferior structure of brainstem

- Regulation of breathing, and other vital activities Module 12.3: Protection of the Brain

Three features protect delicate brain tissue:

1. – three layers of membranes that surround brain

2. Cerebrospinal fluid (CSF) – fluid that bathes brain and fills cavities

3. Blood-brain barrier – prevents many substances from entering brain and its cells from blood

• Cranial meninges

– composed of three layers:

superficial to deep:

epidural space

a.

subdural space

b. (weblike)

subarachnoid space (CSF filled)

c. (in contact with brain tissue)

• Four ventricles within brain (1st & 2nd = lateral ventricles, 3rd and 4th ventricle connected via cerebral aqueduct)

continuous with central canal of spinal cord

Lined with cells

Filled with

• CSF (similar to plasma)

Brain Protection

The Ventricles and Cerebrospinal Fluid

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Produced by

Reabsorbed by arachnoid villi (granulations)

~800ml produced daily, only 150ml at any time

Cushions brain, maintains temp., removes wastes, provides buoyancy

Infectious Meningitis

• Potentially life-threatening infection of meninges in subarachnoid space; inflammation occurs, causing classic signs: headache, lethargy, stiff neck, fever

• Diagnosis – examination of CSF for infectious agents and white blood cells (cells of immune system); bacteria and viruses are most common causative agents:

– generally mild; resolves in 1–2 weeks

– can rapidly progress to brain involvement and death; aggressive antibiotic treatment necessary; some most common forms are preventable with vaccines

Module 12.4: The Spinal Cord

• – composed primarily of nervous tissue; responsible for both relaying and processing information (reflexes)

• Spinal Meninges (similar to cranial meninges)

space – space between meningeal dura and walls of vertebral foramina; filled with veins and adipose tissue; cushions and protects spinal cord

space – between arachnoid and pia mater; filled with CSF; base of spinal cord contains a large volume of CSF useful site for withdrawing samples laboratory testing

The Spinal Cord

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Epidural Anesthesia and Lumbar Punctures • Epidural (spinal) anesthesia – local anesthetic medication is injected into epidural

space through an inserted needle

• Causes “numbing” (inability to transmit motor or sensory impulses) of nerves extending off spinal cord below level of injection

• Commonly given during childbirth and other surgical procedures

• (spinal tap) – needle inserted into subarachnoid space between L4 and L5; avoids possibility of injuring SC

• CSF is withdrawn for analysis; used to assess conditions like meningitis, encephalitis and multiple sclerosis

• – extends from between L1 and L2 to coccyx

- composed of spinal pia mater

• = bundle of spinal nerves contained in vertebral canal

• Spinal nerves (PNS); carry sensory and motor impulses to and from SC

• Posterior (dorsal) nerve root –

• Anterior (ventral) nerve root -

• Butterfly (H) -shaped spinal matter is surrounded by tracts of white matter;

– filled with CSF; seen in center of spinal cord

• Anterior (ventral) horn – motor neurons to skeletal muscle

• Posterior (dorsal) horn – sensory information

• Lateral horn – motor, visceral efferent (ANS) Module 12.5: Role of the CNS in Sensation

• Role of Cerebral Cortex in Sensation, S1 and Somatotopy:

relays most incoming information to primary somatosensory cortex (S1) in postcentral gyrus

External Spinal Cord Anatomy

Internal Spinal Cord Anatomy

General Somatic Senses

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Each part of body is represented by a specific region of S1, a type of organization

called

More S1 space is dedicated to hands and face; represents importance of manual dexterity, facial expression, and speech to human existence

Phantom Limb Pain

• Phantom limb – occurs after amputation of limb, digit, or even breast; patients perceive body part is still present and functional in absence of sensory input; small percentage develop phantom pain (burning, tingling, or severe pain) in missing part

• Difficult to treat due to complex way CNS processes pain; supports idea that S1 has “map” of body that exists independently of PNS

• Over time, map generally rearranges itself so body is represented accurately; phantom sensations decrease

Module 12.6: Role of the CNS in Voluntary Movement

• Role of Cerebral Cortex in Voluntary Movement:

Primary motor cortex is organized somatotopically; certain body regions have disproportionately more cortical area devoted to them (especially lips, tongue, and hands); signifies importance of vocalization and manual dexterity to human survival

Parkinson’s Disease

▪ One of most common movement disorders

▪ Hypokinetic = movement is difficult to initiate and once started, difficult to terminate

▪ Symptoms – minimal facial expression, shuffling gait, no arm swing, resting tremor

▪ Cause – degeneration of -secreting neurons of substantia nigra; genetics suspected in ~10% of cases

▪ Treatment – medications that increase level of dopamine

Role of Brain in Voluntary Movement

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Module 12.7: Role of the CNS in Maintenance of Homeostasis

is defined as maintenance of a relatively stable internal environment in face of ever-changing conditions

• Homeostatic functions include maintaining fluid, electrolyte, and acid-base balance; BP; BG and [O2]; biological rhythms; and body temperature

Endocrine system secretes into blood; regulates functions of other cells (long term)

Nervous system sends ; excite or inhibit target cells (immediate)

• Autonomic nervous system ( )

- Maintain vital functions (HR, BP, digestion)

- Although ANS is a component of PNS, mainly controlled by hypothalamus

• is one of few vital functions not under ANS control; regulated by Pons and Medulla

• Body Temperature – reg. by

Fever

• Elevation of body temperature can accompany variety of infectious and noninfectious conditions

• Due to (chemicals) secreted by cells of immune system and by certain bacteria; cross BBB and interact with hypothalamus (control temp.)

• Pyrogens increase hypothalamic set point to higher temperature; feedback loop triggers shivering and muscle aches due to increased muscle tone; VC of blood vessels to skin

• (acetaminophen and aspirin)- work by blocking formation of pyrogens; hypothalamus returns to normal set point

Role of CNS in Maintenance of Homeostasis

Homeostasis of Vital Functions

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Dementia

• Patients with dementia exhibit a progressive loss of recent memory, degeneration of cognitive functions, and changes in personality

• No proven method for prevention or cure of dementia exists; some drugs may slow progression of Alzheimer’s disease in certain patients but do not reverse changes that already exist; ineffective in other forms of dementia

• Common (most to least) forms of dementia include:

•

• Neurofibrillary tangles (aggregates of proteins in neurons), senile plaques (extracellular deposits of specific protein around neurons)

• Vascular dementia

• Lewy body dementia

• Pick’s disease

Two basic types of memory:

1. (fact) – readily available to consciousness

ex. – phone number, a quote, or pathway of corticospinal tracts

2. (procedural or skills) – unconscious association

ex. – how to enter phone number on a phone, how to move your mouth to speak, and how to read this chapter

• Declarative and nondeclarative memory classified by length of storage time

memory – stored only for a few seconds; is critical for carrying out normal conversation, reading, and daily tasks

(working) memory – stored for several minutes; allows you to remember and manipulate information with a general behavioral goal in mind

memory – a more permanent form of storage for days, weeks, or even a lifetime

Learning and Memory

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Chapter 13: The Peripheral Nervous System

PNS: 1. (Afferent)

a. Somatic Sensory Div. (special senses, skin, skeletal muscle)

b. Visceral Sensory Div. (viscera)

2. (Efferent)

a. Somatic Motor Div. (to skeletal muscle)

b. Visceral Motor Div. (ANS) Module 13.1: Overview of the Peripheral Nervous System

• Peripheral nerves = axons of many neurons bound together by CT

nerves – contain both sensory and motor neurons

Sensory nerves –

Motor nerves -

2 types of nerves:

Spinal nerves ( )

Cranial nerves ( )

• Spinal nerves

(ventral) root - motor neurons from anterior horn

(dorsal) root - sensory neurons from posterior horn

- collection of cell bodies of sensory neurons

• Structures associated with spinal nerves: Epineurium – outermost layer of CT, holds motor and sensory axons together

– CT that surrounds fascicles (bundles of axons)

– CT surrounds individual axon

Overview of Peripheral Nerves

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Module 13.2: The Cranial Nerves

• Sensory only cranial nerves:

(I)

(II)

(VIII)

Oculomotor (III) – 4 of extraocular muscles, pupil constriction, opens eyelid, lens shape

(IV) – 1 of extraocular muscles (sup. oblique)

(VI) – 1 of extraocular muscles (lat. rectus)

Accessory (XI) – larynx, trapezius, SCM

Hypoglossal (XII) – tongue muscles

(V) – supplies skin of face, muscles of mastication

(VII) – facial expressions, taste ant. 2/3 tongue

Glossopharyngeal (IX) – taste post. 1/3 tongue, BP changes, swallowing, salivary glands

(X) – thoracic and abdominal viscera, main nerve of PSN

Trigeminal Neuralgia (tic douloureux)

- Chronic pain syndrome

- Involves one or more branches of trigeminal nerve (CN V)

- Certain stimuli may trigger attacks (chewing, light touch, vibrations)

- Cause: idiopathic

- Treatment: pain medications, sever nerve

The Sensory Cranial Nerves

The Motor Cranial Nerves

The Mixed Cranial Nerves

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Bell’s Palsy

Facial nerve (CN VII)

- Cause: virus, tumor, trauma, or idiopathic

- Weakness or complete paralysis of facial muscles (unilateral)

Treatment - anti-inflammatory medication, antiviral medication, PT, and surgery; even without treatment,

Many individuals recover function of paralyzed muscles in about 3 weeks Module 13.3: The Spinal Nerves

Cervical Plexus

-

Brachial Plexus

-

-

- Musculocutaneous n.

- Median n.

-

Lumbar Plexus

- Obturator n.

-

Sacral Plexus

-

Structure of Spinal Nerves and Spinal Nerve Plexuses

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A Hiccup Cure That Really Works

• Hiccups –spasms of diaphragm that cause a forceful inhalation of air

• Phrenic nerve remedy:

• Place fingers ~ 1 cm lateral to vertebral column level of C3-C5

• Apply firm pressure to muscles of neck that overlie phrenic nerve until hiccups stop, in about 5–10 seconds

Lumbar Plexus

• Left and right lumbar plexuses are derived from anterior rami of L1–L5; anterior to vertebrae; embedded deep within psoas muscle; branches innervate pelvic structures and lower extremity after splitting into 2 divisions

Module 13.4: Role of PNS in Sensation

• Based on location of stimuli they detect:

– detect stimuli originating from outside body (thermoreceptors, chemoreceptors, photoreceptors)

– detect stimuli originating from within body itself (chemoreceptors)

- depolarize in response to anything that mechanically deforms tissue (vibration, light touch, stretch, and pressure)

• Merkel cell fibers

Found in epidermal ridges of especially fingertips

Detect discriminative touch stimuli (object form and texture)

• Tactile corpuscles ( corpuscles)

Dermal papillae

• Ruffini endings

• Lamellated corpuscles ( corpuscles)

Classification of Sensory Receptors

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Module 13.6: Reflex Arcs: Integration of Sensory and Motor Function

• Reflexes – pre-programmed, automatic responses to stimuli; arc; usually protective negative feedback loops

Reflexes begin with a sensory stimulus and finish with a rapid motor response

Neural integration between sensory stimulus and motor response occurs in CNS, at spinal cord or brainstem

• Reflexes can be classified by at least two criteria:

Number of synapses that occur between neurons involved in arc

Type of organ in which reflex takes place, either visceral or somatic

• Simplest reflex arcs ( reflexes) involve only a single synapse within spinal cord between a sensory and motor neuron; more complicated types of reflex arcs ( reflexes) involve multiple synapses

▪ Simple stretch reflex

Body’s reflexive response to stretching of muscle to shorten it back to within its “set” optimal length

▪ Flexion (withdrawal) reflex:

Reflex Arcs

Types of Reflexes

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Amyotrophic Lateral Sclerosis

- degeneration of cell bodies of motor neurons in anterior horn of SC, upper motor neurons in cerebral cortex; cause of degeneration is unknown at present; many factors likely play a role

• Most common early feature of disease is muscle weakness, particularly in distal muscles of limbs and hands; over time weakness spreads to other muscle groups; upper motor neuron symptoms also develop

• Death usually in ~5 years of disease’s onset

• Although intensive research efforts are ongoing, at this time there is no cure or treatment that prevents disease progression

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Chapter 14: The Autonomic Nervous System and Homeostasis

ANS = involuntary arm of PNS - - two divisions:

(SNS) (PSN)

- maintain homeostasis Module 14.1: Overview of the Autonomic Nervous System

• Motor divisions of PNS:

division à skeletal muscle (conscious control)

motor division à smooth muscle, cardiac muscle, and glands (involuntary)

• - ANS motor neurons require a two-neuron circuit:

1. Preganglionic neuron – 2. Postganglionic neuron –

Main structural and functional differences between SNS and PSN:

• nervous system – preganglionic axons are usually short and postganglionic axons are usually long

• nervous system – preganglionic parasympathetic axons are long while postganglionic axons are short

Sympathetic nervous (SNS)

• thoracolumbar division

• Sympathetic ganglia located near SC

• “ ” division of ANS; prepares body for emergency situations

Comparison of Somatic and Autonomic Nervous Systems

Divisions of the ANS

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Parasympathetic nervous system

• Craniosacral division

• Cranial nerves à head and neck, thoracic viscera, and most abdominal viscera

• “ ” division; role in digestion and maintain body’s homeostasis

at rest

• Postganglionic neurons located near target organ; requires only a short axon to connect

Module 14.2: The Sympathetic Nervous System

Effects of SNS on target cells:

– directed at ensuring survival and maintenance of homeostasis during time of physical or emotional stress

• Cardiac muscle cells à Increase and force of contraction

• of blood vessels à digestive, urinary, & integumentary

• Dilation of

• to skeletal & cardiac muscle

• Constriction of sphincters à urinary & digestive

• Relaxation of smooth muscle of digestive tract

• Dilation of

• sweating Module 14.3: The Parasympathetic Nervous System

“ ” division of ANS

• Role in maintenance functions - digestion and urine formation

• Craniosacral divison

Effects of SNS on Target Cells

Gross and Microscopic Anatomy PSN

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• PSN cranial nerves – oculomotor (CN III), facial (CN VII), glossopharyngeal (CN IX), and vagus (CN X) nerves

• Cardiac muscle cells - HR & BP

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• SMC contraction along digestive tract – increased

• of digestive and urinary sphincters à promotes urination and defecation

Engorgement of penis or clitoris

salivation, lacrimation, and digestive enz.

Module 14.4: PNS Maintenance of Homeostasis

• Sympathetic and parasympathetic divisions work together to keep many of body’s functions within their normal homeostatic ranges

dual innervation

Dual innervation allows SNS to become dominant and trigger effects that maintain homeostasis during physically demanding periods

PSN division regulates same organs, preserving homeostasis between periods of increased physical activity

Postural Orthostatic Tachycardia Syndrome (POTS)

- Increase in heart rate (known as tachycardia) when an individual moves from lying or sitting down to standing up; VD à BP drop due to drop due to gravity

Symptoms (from low blood pressure)

- include dizziness and lightheadedness

- fatigue and thirst

- shortness of breath, chest pain, cold extremities, and muscle weakness Cause: excessive SNS activity

Treatment: dietary modifications such as increasing water and salt intake

Effects of PSN on Target Cells

Interactions of Autonomic Divisions